It is well known in the art that dynamoelectric machines generally include a stator and rotor, with one typical design including a cylindrical rotor which rotates within an annular stator. Also, it is well known that such a stator will include a plurality of windings comprising electrical wire which are laid in a plurality of channels formed by winding slots along the inner periphery of a plurality of stacked annular plate-type stator laminations.
Performance of the dynamoelectric machine of this design can be improved by skewing the stator, i.e. angularly re-positioning successive laminations from the top to the bottom of the lamination stack. Typically, the entire stack of laminations will be skewed one slot width, such that the top lamination is re-positioned one slot clockwise or counterclockwise from the corresponding slot in the lamination at the bottom of the stack, with the intervening laminations making a graduated transition between these two end positions.
In the prior art, automatic insertion type winding machines for automatically winding the stator slots require that the slots be aligned and that the stator be non-skewed. As best known to the inventor herein, there are no automatic insertion type winding machines which can automatically wind a skewed stator lamination stack with skewed winding slots. Thus, it is presently the practice to manufacture stators by first stacking the laminations in a concentric, aligned fashion, for winding, each of the laminations having a pair of slots with the slots positioned at opposite sides of the lamination and near the outer periphery thereof. These slots are generally circular slots and align as the laminations are stacked. A pair of pins or bolts are typically used to position the laminations as they are stacked such that the slots in the laminations are fit over the bolts as the laminations are stacked.
With the stack of laminations thus formed, the winding slots align to create a substantially straight, tunnel-like, winding channel for automatic insertion of the windings. After the stator is wound, pressure is applied to opposite sides of the bolts in a direction tangential to the stator, and at opposite ends thereof, which thus skews the laminations into the desired orientation. After skewing, the stator is welded and the bolts are then removed.
Although this technique works satisfactorily for smaller size stators, i.e. stators below a 280 frame size, this technique will not work for larger stators. There are several reasons for this, perhaps the most important of which is that the alignment bolts must "go over the hill". By that is meant that the bolts must generally twist in a helical fashion with the center of the bolts moving radially outwardly and the ends of each bolt rotating with respect to each other. This contortion of the bolt is caused by the fact that the slots in each of the laminations remain the same radial distance from the center of the stack as the laminations are skewed, so that the series of slots transforms from a straight line into an arc. As the bolt remains within the series of slots, the bolt must contort to follow this transformation in the slot pattern. The bolts which hold the laminations in alignment must thus be rigid enough to maintain the alignment of the laminations, but at the same time flexible enough to accommodate the helical contortion placed on it. For the larger frame sizes, this combination of rigidity and flexibility is virtually impossible to achieve. Therefore, for this and other reasons, the larger frame sizes are typically wound by hand after the lamination stack has been assembled in a skewed orientation.
It should be also noted that the inventor herein is aware of the fact that skewed rotors have been produced in the prior art. Those rotors of which the inventor is aware utilized plate-type laminations much as with the stator design discussed herein, except that there was no winding of the rotors with electrical wire and the rotor laminations were initially stacked in a skewed orientation (much as is presently done for larger frame size stators, as described above). In order to maintain the alignment of the individual laminations as they were stacked in a skewed orientation, rotor laminations were made with elliptical slots on opposite sides thereof such that they could be slipped over a pair of alignment bolts. However, it should be emphasized that these rotor laminations were initially assembled in a skewed orientation, were not wound with electrically conductive wire, and thus the alignment slots did not teach or suggest that they would provide any advantage in transforming a stack of concentrically oriented laminations into a stack of skewed laminations.
In order to solve these problems inherent in the prior art with manufacturing skewed stators, and especially for larger frame sizes, the inventor herein has succeeded in developing an alignment structure and technique which permit stacking of stator laminations in an aligned fashion, with the laminations being stacked concentrically to facilitate winding by automatic winding equipment, and then skewing the wound lamination stack in a controlled manner in such a way as to eliminate any contortion of bolts. Therefore, for the first time, a stator lamination stack may be automatically wound and then skewed for the larger frame size dynamoelectric machines which were heretofore first skewed and then hand wound.
In a first embodiment, alignment bolts are used with the stator laminations each having a pair of alignment slots which are generally elliptical in shape. Thus, as the laminations are stacked over the bolts, they are held in concentric alignment for winding, and then opposing tangential forces exerted at the ends of the bolts which skew the stator. In the skewing process, the slot permits controlled relative movement between the laminations and the bolts in a radial direction such that there is no relative force exerted on the bolts by the laminations, or vice versa. Instead, the bolt is free to move within the generally elliptical slot. In order to increase the bearing surface and facilitate their relative sliding movement, flats may be formed along opposite sides of the bolt to match the sides of the slots. To the extent that flats are used, the length of the elliptical alignment slots should be increased by the length of each flat. Although desirable, it is not believed that the flats are necessary to achieve the controlled skewing without contortion of the alignment bolts.
In an alternative embodiment, the alignment slots are not used but instead projections are formed on opposite sides of each lamination such that they align as the laminations are stacked concentrically. In order to ensure that the laminations remain concentric, alignment channels may be used to maintain the projections in their proper orientation for concentric alignment. Then, in order to skew, the channels are pivoted, with the outer walls of the projections and the inner walls of the channel being formed at such an angle that the projections may move radially with respect to the channel, with the projections canting as they are skewed. Depending upon the position of the particular stator lamination with respect to the stack, the projections will retract from within the channel and cant, but will always remain in contact with the mouth of the channel such that they are physically restrained thereby and held in place. Thus, controlled relative movement in a radial direction and canting is permitted between the channel and the projections in order to achieve a uniformly skewed stator.
While the principal advantages and features of the present invention have been briefly described above, a fuller understanding of the invention may be attained by referring to the drawings and detailed description of the preferred embodiment which follow.